Segments and Geographic Information - Total Revenue from Company's Next Largest Client (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue, Major Customer [Line Items]
Amount	$ 1,286,340	$ 1,327,523	$ 1,263,460
Customer Concentration Risk [Member] | Next Largest Client [Member]
Revenue, Major Customer [Line Items]
Amount	$ 62,980	$ 70,255	$ 73,226
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Next Largest Client [Member]
Revenue, Major Customer [Line Items]
% of Revenues	4.90%	5.30%	5.80%
Americas [Member] | Customer Concentration Risk [Member] | Next Largest Client [Member]
Revenue, Major Customer [Line Items]
Amount	$ 62,980	$ 70,255	$ 73,226
Americas [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Next Largest Client [Member]
Revenue, Major Customer [Line Items]
% of Revenues	6.00%	6.60%	7.00%
EMEA [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Next Largest Client [Member]
Revenue, Major Customer [Line Items]
% of Revenues	0.00%	0.00%	0.00%